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‘Shocking’ discovery boosts chance of life on Europa

By Jenny Hogan

Scientists simulating meteorite impacts on the frozen oceans of Europa have made an electrifying discovery, which raises the chances of finding life on Jupiter’s moon.

Jerome Borucki, at the NASA Ames Research Center in California, and his colleagues fired aluminium bullets into a block of ice. They found that when the bullet impacted, sensors embedded in the ice detected an electric shock. A second, and much larger, electrical discharge was observed a few moments later.

A shell of ice many kilometres thick encases the surface of Europa and scientists speculate that liquid water – and therefore life – might lie beneath. Evidence for the presence of the molecular building blocks for life comes from the yellow-brown stains seen on the ice by the Galileo probe.

“Europa is a high priority target for exploration because the key ingredients for life seem to be there. But even if you have the ingredients, the question is, is there a spark that creates the first organic molecules?” says Ron Greeley, a planetary scientist at the Arizona State University.

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Borucki’s bullet experiments suggest meteorite impacts might have provided that spark. The electric shock had gone undetected because no-one had put sensors below an impact crater before, he told New Scientist. The team think the current is caused by the movement of protons as the ice cracks.

Methane and ammonia

In the 1950s, Stanley Miller, now at the University of California in San Diego, showed that shooting an electric current through a mixture of water, methane and ammonia created complex organic molecules. Amino acids, the building blocks of proteins, were among the products.

Methane and ammonia are likely to be present in Europa’s ice and the energy pumped into the ice by a meteorite impact will melt it. Shock this mixture with electricity, says Borucki, and complex molecules should form.

But this still needs to be tested in the laboratory. So far the experiments have used only pure water ice, cooled to a chilly -196°C to simulate conditions on Europa.

The bullets used are about a centimetre across and were fired at the ice at a speed of six kilometres per second. This is the equivalent to a kilometre-sized asteroid crashing into the moon at about 24 km/s.

“We do see a handful of very large craters on Europa, and there would have been a lot of energy associated with those,” comments Greeley. “These new results are exciting.”

Greeley has been appointed by NASA to set the scientific priorities of Jupiter’s Icy Moon Orbiter. This probe, which has recently been allocated funding, will visit Europa and two of Jupiter’s other moons, Callisto and Ganymede. A lander may be sent to the surface of Europa to look for organic matter. But it will be a long wait – Greenley estimates the earliest launch date for the mission to be 2011.